XEP-0316: MUC Eventing Protocol

Abstract:

This specification defines semantics for using the XMPP publish-subscribe protocol to broadcast state change events associated with a Multi-User Chat (MUC) room. This profile of pubsub therefore enables a chatroom to function as a virtual pubsub service, easing the discovery of syndicated data and event notifications associated with such a room.

WARNING: This document has been automatically Deferred after 12 months of inactivity in its previous Experimental state. Implementation of the protocol described herein is not recommended for production systems. However, exploratory implementations are encouraged to resume the standards process.

When new information is available about the multimedia session (say, calling into a conference "bridge" or starting a Jingle (XEP-0166) [5] session to add a video feed), a multimedia engine might capture that event and inform the chatroom by means of a backend API. The chatroom itself then generates an event notification. That is, a chatroom does not publish events, instead it simply generates them based on data of interest. As a result, everyone in the room who is interested in that kind of data will receive a notification about the event:

But how do the occupants tell the room that they are interested in knowing what about conference-info events? Whereas generic pubsub services require an explicit subscription to a conference-info node, MEP services support the "filtered-notification" feature from XEP-0060 and obviously share presence (since MUC is based on directed presence in the room) so the "auto-subscribe" feature also applies.

That chatroom knows to send conference-info notifications to crone1@shakespeare.lig because when the room unpacks the value of the 'ver' attribute ("054H4A7280JuT6+IroVYxgCAjZo=") in accordance with XEP-0115, it discovers that her client advertises a service discovery feature of "urn:ietf:params:xml:ns:conference-info+notify", where the "+notify" suffix indicates interest in receiving notifications related to the protocol that precedes the suffix. The server can verify this support if needed by sending a service discovery request to crone1's full JID (see XEP-0115 for details).

The foregoing section described how the room itself can inform the occupants about data of interest. However, in MEP any particular occupant can also publish information. An occupant does so by sending a publish-subscribe publish request to the occupant's Occupant JID <room@service/nick> (similar to the way in which publishing via PEP happens by sending a request to the user's bare JID <user@host>). For instance, the following example shows how a room occupant would inform the other occupants about an event of interest.

Note: Publishing to an occupant's MEP node happens by sending an explicit publish request to the Occupant JID. Publishing to a user's PEP node MUST NOT trigger a MEP publish request, because PEP and MEP are separate pubsub contexts.

As a result, everyone in the room who is interested in that kind of data will receive a notification about the event (note that even the publisher receives the event, if they have advertised interest in the payload type):

By default, the use of directed presence is used to establish a MEP subscription to the chatroom's eventing data. In order to filter which notifications are sent by the MEP service, the contact's client includes extended Entity Capabilities (XEP-0115) [6] information in the directed presence notifications it sends to the chatroom. Because the MEP-enabled room supports the "filtered-notifications" feature, it sends only those notifications that match the occupant's expressed notification preferences.

Default the 'send_last_published_item' configuration option to on_sub_and_presence (i.e., send the last published item on subscription and on receipt of presence), treating the receipt of directed presence as equivalent to a subscription.

A PEP service MAY support other use cases, affiliations, access models, and features, but such support is OPTIONAL.

If a chatroom supports MEP, it MUST advertise that fact in its responses to Service Discovery (XEP-0030) [7] information ("disco#info") requests by returning an identity of "pubsub/mep" and the relevant pubsub features:

Appendix C: Legal Notices

Copyright

Permissions

Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).

Appendix D: Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.

Appendix E: Discussion Venue

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Appendix F: Requirements Conformance

The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".

8. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.

9. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.